Bent the Hoe Boom Cylinder

[Wayne_Freeman]

My Kubota L3400 has an older 4690 backhoe that has done quite well until today when I bent the boom cylinder rod. I was digging some riprap around my spillway mouth and had the bucket four feet below the ground surface when I realized the boom could not come back up and the cylinder was visibly bent. The new cylinder is on order but I would like to figure out what I did to cause this failure. Searching this site I have found where dipper and crowd cylinders have bent when digging close in to the tractor but nothing concerning the boom cylinder. Does anyone have any information to share?

 

[john_bud]

If it was only bent a little, you can straighten them out in a hydraulic press. That's much cheaper than replacement, but may not always work.

I would have replaced with a cylinder that had a 1/4 to 1/2" larger rod diameter and maybe a 1/2" larger cylinder diameter also. But I'm a "more power" type.

jb

 

[Wayne County Hose]

How about some pictures? Did you buy a complete cylinder from Kubota?

Rods usually bend when the rod is extended and something tries to push it back into the cylinder.

 

[Wayne_Freeman]

Attached is a picture of my bent boom cylinder. I took it to Savannah Ga. yesterday to a repair shop and found out pretty quick the repair was as much or more than a new one. Cost is $300 plus shipping from Messicks. Wonder if there is a cheaper generic somewhere? I have dug a ton of stumps with no problems. This time I was digging 4 feet below ground level and obviously did something wrong?

 

[crashz]

If you had the stick perfectly straight down in the hole, with the boom at almost 90 degress to it, and then uncurled the buckt against bottom, the weight of the tractor could be lifted by the bucket, and forces would concentrate at the extended boom cylinder. This is the only way that I can see enough down pressure to bend the boom cylinder.

 

[KennyV]

Did you move or reposition the tractor with the stick down in the hole?

 

[john_bud]

Attached is a picture of my bent boom cylinder. I took it to Savannah Ga. yesterday to a repair shop and found out pretty quick the repair was as much or more than a new one. Cost is $300 plus shipping from Messicks. Wonder if there is a cheaper generic somewhere? I have dug a ton of stumps with no problems. This time I was digging 4 feet below ground level and obviously did something wrong?

Check

surplus center dot com

baileynet.com (need a tax tag to order from them. Maybe Wayne the hose guy can order for you and have drop shipped (at a profit for him)?

2 1/2 bore 24" stroke cylinders are in the 150 to 250 range. So the 300 is not out of the norm.

 

[kthompson]

Wayne, you are not that far from Agri Supply in Florence. I would check with them on cylinder. Be sure they have it in stock before you drive there. They do have good web site, just look for Agri Supply. They may have store in Georgia closer to you not sure.

 

[rback33]

Your pricing is not bad for that type of cylinder. Ouch for sure though...

 

[Wayne_Freeman]

I posted this in the Kubota forum as well and got some great information. Take a look http://www.tractorbynet.com/forums/kubota-owning-operating/137576-bent-cylinder.html

 

[Eagleview]

As the picture clearly shows , the rod was not fully extended , taking into account the paint line on the ram and the length of the tube . Nor is it possible that it could have been as you say the bucket was below grade by 4' . The boom could not have been fully up . Is it possible the ram came into contact with the spoils from the hole ? Did the ram bend up or down ?

 

[Wayne_Freeman]

I think the rod was fully extended when the damage occurred and would pull in a few inches.

 

[Eagleview]

That would mean the boom was at full height when the damage occured .

 

[Wayne_Freeman]

The boom cylinder was fully extended and the bucket was down in the hole. I had to take the cylinder loose at one end just to drag the bucket up to ground level because the bent cylinder would not retract.

 

[Eagleview]

You may have found your problem . It must be a very strange arrangement that would have the boom fully up , and the bucket 4' down a hole instead of being at least 2 feet in the air .

 

[Wayne_Freeman]

What I meant to say was when the boom cylinder is extended the boom is down. To raise the boom fully the boom cylinder is fully retracted

 

[john_bud]

You may have found your problem . It must be a very strange arrangement that would have the boom fully up , and the bucket 4' down a hole instead of being at least 2 feet in the air .

The BH boom cylinder is above the boom, not below it. It is designed to give higher digging forces at the expense of lower lift force.

My boom cylinder is like yours, UNDER the boom and is extended to raise. The small hoe's are the other way around to maximize dig with small cylinders. Obviously, they are engineered right to the edge.

jb

 

[Eagleview]

Ahh , i see it all , thank you . So any effort that would try and lift the rear of the machine would try and bend the ram . I do'nt understand why they would use the back side of the piston with it's lower capacity to do the heaviest task , lifting .
Please accept my apology Wayne , i was'nt aware the ram was on top .

On edit , i wonder why it would not work the same as other backhoes , the ram underneath should have enough downforce .

 

[Wayne_Freeman]

No problem. Thanks for your input!

 

[john_bud]

On edit , i wonder why it would not work the same as other backhoes , the ram underneath should have enough downforce .

In a word --> Marketing driven low cost engineering.


They use a smaller cylinder to get the cost down but use the "big end" to get the force numbers up to impress the buyers.


jb